http://prntscr.com/n6c377
You can't unlock this, because this is a Jira managed field and can't be modified.
Locked > This custom field is managed by JIRA Software and cannot be modified.
HI @Elena Sholk
Don't do it...as due to some reason Application has been locked by default and if you change it then may be the core functionality will not work as expected.
Still if you want you can do it, please have a look at the below article.
https://confluence.atlassian.com/jirakb/how-to-unlock-a-locked-jira-software-field-779158866.html?_ga=2.221121624.1122258548.1554096634-1229953293.1554096634
The screenshot is of Jira Cloud, where you don't have the access to be able to unlock anything. Not a bad thing - means you can't break it (the lock is there for a good reason)
It looks like you're new here. Sign in or register to get started.